The present invention relates to nerve surveillance systems and to cannulae systems for use in minimally invasive spinal surgery.
A significant danger of performing intervertebral operations or accessing an intervertebral space during spine surgery is that of inadvertently contacting or damaging the para-spinal nerves, including the exiting nerve roots, traversing nerves and the nerves of the cauda equina. The exact location of these para-spinal nerves can not be determined prior to the commencement of surgery. Moreover, intervertebral spaces in the spine have other sensitive nerves disposed at locations which are not entirely predictable prior to insertion of the surgical tool into the intervertebral area. Accordingly, the danger of pinching or damaging spinal nerves when accessing an intervertebral space has proven to be quite limiting to the methods and devices used during minimally invasive spinal surgery. In addition, as cannulae are received through the patient""s back, such as when performing minimally invasive spinal surgery, minor blood vessels are ruptured, thereby blocking the surgeon""s vision inside the intervertebral region after the cannula has been inserted.
The present invention provides nerve surveillance probes which are adapted to assist the surgeon in identifying the presence and location of para-spinal nerves as the probe is advanced during minimally-invasive surgery, thus providing a device for guiding the path of other surgical instruments to be inserted into this intervertebral space. In a preferred aspect of the present invention, an expandable tip cannula system is provided which functions both as an access portal for spinal surgery and as a system for nerve surveillance such that the presence and relative position of para-spinal nerves can be detected as the expandable tip cannula is inserted through the patient""s facia and para-spinal musculature. An advantage of determining the position of a para-spinal nerve with respect to the distal tip of the cannula in particular is that the para-spinal nerve can be avoided or gently moved out of the surgeon""s way while inserting the cannula. Accordingly, in a preferred aspect, the present invention provides a cannulated system which is adapted to assist the surgeon in guiding the path of surgical instruments received into the intervertebral space, while identifying the presence and location of para-spinal nerves as the cannula is advanced to a patient""s intervertebral space during minimally invasive surgery.
Optionally, the present nerve surveillance expandable tip cannula may also be adapted to selectively electrically induce cauterization of severed blood vessels when the cannula or other surgical instruments sever small blood vessels when they are inserted percutaneously into the patient and are advanced along a path into the patient""s intervertebral space. An additional advantage of the present cannula system therefore is that, prior to piercing the annulus of an intervertebral disc, vessels on the surface of the disc may be cauterized to assure clear vision inside the disc after surgical entry is made.
In one embodiment, the present expandable tip nerve surveillance cannula preferably comprises a hollow tubular body with a expandable tip portion mounted at its distal end. In a preferred aspect of the invention, the expandable tip portion comprises a plurality of generally triangular shaped petals which are held together in a radially-inwardly tapering arrangement by breakable seals disposed between adjacent petals. Since the expandable tip portion of the cannula tapers to a narrow blunt end, the cannula can be easily pushed through the patient""s facia and spinal musculature using blunt dissection, while minimizing the amount of cutting and tearing of such structures.
Alternatively, a central electrode can be disposed on a central obturator passing though the cannula and a second electrode can be disposed on a distal end of a second cannula, wherein the second cannula is used to open the petals.
An obturator shaft which is slidably received within the hollow tubular cannula body provides support for the cannula, giving the cannula sufficient strength such that the cannula can be inserted percutaneously through the patient""s facia and para-spinal musculature. Preferably, the obturator has a large solid handle which allows the surgeon to grasp and push the cannula through the resistance of the facia and para-spinal musculature.
After the cannula has been inserted and is resting on the patient""s annulus, a inner cannula or rod which is slidably received within the cannula is then used to separate the breakable seals, opening the petals radially outwards to a distance sufficient to provide access for surgical instruments passing therethrough.
In some preferred aspects, an electrode is disposed in each of the petals, and most preferably at or near the distal end of each of the petals. In other aspects of the invention, a plurality of electrodes are radially disposed about the distal end of the obturator and the electrodes protrude out of a small hole defined by truncated petals, as will be explained.
In various aspects of the present invention, the electrodes can be powered at a low level to thereby sense the position of a para-spinal nerve through continuous real time electromyographic monitoring, or alternatively, the electrodes can be powered at a higher level such that they operate to cauterize blood vessels. Safety systems ensure that power levels sufficient to cause cauterization are not activated if a nerve is sensed to be near the electrodes at the distal end of the cannula.
In alternate embodiments, the present invention comprises an elongated nerve surveillance probe having one or more electrodes at its distal tip. In such aspects, the nerve surveillance probe is preferably advanced to the patient""s intervertebral space through a cannula. In other alternate embodiments, the present nerve surveillance probe is received into the patient through various cannulae and expandable mesh trocars.